The present invention relates to an apparatus for detecting leakage in an evaporated fuel processing system after an internal-combustion engine is stopped.
Various approaches have been proposed for detecting leakage in an evaporated fuel processing system after an internal-combustion engine is stopped. According to one of such approaches (for example, refer to the Japanese Patent Application Unexamined Publication No. 11-336626), an evaporated fuel processing system is placed under a negative pressure after the engine is stopped. It is determined whether the system has leakage based on a change in the pressure of the system.
A canister is provided in the evaporated fuel processing system for adsorbing evaporated fuel generated in a fuel tank. The canister has a passage that communicates with the atmosphere, in which an open-to-atmosphere valve (which is referred to as “vent-shut valve”) is disposed. The vent-shut valve is usually kept in an open state. When leakage determination for the evaporated fuel processing system is performed, the vent-shut valve is opened/closed in accordance with a control signal from a control unit.
If the pressure in the evaporated fuel processing system becomes higher than a predetermined positive pressure, or if the pressure in the system becomes lower than a predetermined negative pressure, the vent-shut valve of the canister hardly opens. If the vent-shut valve does not open, the leakage determination cannot be stably performed.
Thus, there is a need for an apparatus and a method capable of prohibiting the leakage determination when a state in which the vent-shut valve of the canister does not open is detected.